Off-axis camshaft phaser

ABSTRACT

A variable camshaft timing system, includes a camshaft phasing mechanism that selectively changes an angular position of an input relative to an output; a first camshaft phaser sprocket, coupled with the input of the camshaft phasing mechanism, configured to engage a first endless loop that communicates rotational force from a crankshaft to the input of the camshaft phasing mechanism; and a second camshaft phaser sprocket, axially spaced from the first camshaft phaser sprocket and coupled with the output of the camshaft phasing mechanism, configured to engage a second endless loop that communicates rotational force from the output of the camshaft phasing mechanism to a camshaft and change the angular position of the camshaft relative to the crankshaft, wherein the camshaft phasing mechanism is mounted about an axis that is different from an axis of camshaft rotation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Patent Application No. 62/621,923 filed on Jan. 25, 2018, the disclosure of which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present application relates to internal combustion engines and, more particularly, to variable camshaft timing of camshafts used with internal combustion engines.

BACKGROUND

Internal combustion engines (ICEs) use one or more camshafts to open and close intake and exhaust valves in response to cam lobes selectively actuating valve stems as the camshaft(s) rotate overcoming the force of valve springs that keep the valves seated and displacing the valves. The shape and angular position of the cam lobes can affect the operation of the ICE. In the past, the angular position of the camshaft relative to the angular position of the crankshaft was fixed. But it is possible to vary the angular position of the camshaft relative to the crankshaft using variable camshaft timing (VCT). VCT can be implemented using camshaft phasing devices (sometimes referred to as cam phasers) that change the angular position of the camshaft relative to the crankshaft. These cam phasers can be hydraulically- or electrically-actuated and are typically directly attached to one end of the camshaft.

However, implementing cam phasers on an ICE involves overcoming a number of challenges. Modern vehicles are allotted increasingly smaller amounts of space for their powertrains, including the ICE. And as the amount of space for powertrains decreases, the flexibility with respect to the size and location of VCT components is beneficial.

SUMMARY

In one embodiment, a variable camshaft timing system includes a camshaft phasing mechanism that selectively changes an angular position of an input relative to an output; a first camshaft phaser sprocket, coupled with the input of the camshaft phasing mechanism, configured to engage a first endless loop that communicates rotational force from a crankshaft to the input of the camshaft phasing mechanism; and a second camshaft phaser sprocket, axially spaced from the first camshaft phaser sprocket and coupled with the output of the camshaft phasing mechanism, configured to engage a second endless loop that communicates rotational force from the output of the camshaft phasing mechanism to a camshaft and change the angular position of the camshaft relative to the crankshaft, wherein the camshaft phasing mechanism is mounted about an axis that is different from an axis of camshaft rotation.

In another embodiment, a variable camshaft timing system includes a camshaft phasing mechanism that selectively changes an angular position of an input relative to an output; a first camshaft phaser sprocket, coupled with the input of the camshaft phasing mechanism, configured to receive rotational force from a crankshaft; and a second camshaft phaser sprocket, axially spaced from the first camshaft phaser sprocket and coupled to the output of the camshaft phasing mechanism, configured to provide rotational force to a camshaft and change the angular position of the camshaft relative to the crankshaft, wherein the variable camshaft timing device is mounted about an axis that is different from an axis of camshaft rotation.

In yet another embodiment, a variable camshaft timing system includes an inner camshaft phasing mechanism that selectively changes an angular position of an inner camshaft phasing mechanism input relative to an inner camshaft phasing mechanism output; a first inner camshaft phaser sprocket, coupled with the inner camshaft phasing mechanism input, configured to engage an endless loop that communicates rotational force from a crankshaft to the inner camshaft phasing mechanism input; and a second inner camshaft phaser sprocket, axially spaced from the first inner camshaft phaser sprocket and coupled with the inner camshaft phasing mechanism output, configured to engage an inner camshaft endless loop that communicates rotational force from the inner camshaft phasing mechanism output to an inner camshaft; an outer camshaft phasing mechanism that selectively changes an angular position of an outer camshaft phasing mechanism input relative to an outer camshaft phasing mechanism output; a first outer camshaft phaser sprocket, coupled with the outer camshaft phasing mechanism input, configured to engage an endless loop that communicates rotational force from the crankshaft to the outer camshaft phasing mechanism input; and a second outer camshaft phaser sprocket, axially spaced from the first outer camshaft phaser sprocket and coupled with the outer camshaft phasing mechanism output, configured to engage an outer camshaft endless loop that communicates rotational force from the outer camshaft phasing mechanism output to an outer camshaft, wherein the inner camshaft and the outer camshaft are concentric.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an internal combustion engine depicting an implementation of a variable camshaft timing system used with a single camshaft;

FIG. 2 is a plan view depicting an implementation of an off-axis camshaft phasing device;

FIG. 3 is a plan view depicting another implementation of an off-axis camshaft phasing device;

FIG. 4 is a perspective view of an internal combustion engine depicting an implementation of a variable camshaft timing system used with concentric camshafts; and

FIG. 5 is a perspective view of an internal combustion engine depicting another implementation of a variable camshaft timing system used with concentric camshafts.

DETAILED DESCRIPTION

A variable camshaft timing (VCT) system includes a camshaft phasing mechanism that selectively changes an angular position of an input relative to an output. The position of the camshaft phasing mechanism, such as a camshaft phaser, is located on a different axis of rotation than the axis of camshaft rotation. In this way, the camshaft phasing mechanism is spaced apart from the camshaft such that the mechanism is located away from the camshaft and can rotate about a different axis of rotation than the camshaft. In the past, camshaft phasing mechanisms have commonly been directly connected to an end of the camshaft. However, given a diminishing availability of space in engine compartments of modern vehicles, some implementations of variable camshaft timing may not permit such a direct connection between the camshaft phasing device and the camshaft. The shape and size of the space in which the vehicle powertrain exists may be more efficiently used if the camshaft phasing mechanism can be mounted apart from the camshaft of the vehicle. Further, at least with respect to VCT systems that use hydraulically-actuated camshaft phasers, camshafts often supply fluid (e.g., engine oil) to the hydraulically-actuated camshaft phaser(s) that are used for actuating the phaser. But fluid pathways in the camshaft may be complex to implement and also be limited by size and shape constraints that hinder flow to a camshaft phasing device. In contrast, when the camshaft phasing mechanism is spaced apart from the camshaft and carried by a wall of the ICE, vehicle designers may be able to increase the size of fluid pathways leading to the mechanism and more easily supply fluid to the mechanism. In addition, positioning the camshaft phasing mechanism at a height located below that of the camshafts and closer to the ground can lower the center of gravity of a vehicle providing benefits, such as better vehicle dynamics.

The system can include a plurality of camshaft phaser sprockets each including radially-outwardly facing gear teeth that transmit rotational energy from the crankshaft to the camshaft. The VCT system can include a first camshaft phaser sprocket coupled with an input of the camshaft phasing mechanism. In some implementations, the first camshaft phaser sprocket can engage an endless loop that communicates rotational force from a crankshaft sprocket to the input of the camshaft phasing mechanism. A second camshaft phaser sprocket that is axially spaced from the first camshaft phaser sprocket is coupled with the output of the camshaft phasing mechanism. The second camshaft phaser sprocket can engage a second endless loop that communicates rotational force from the output of the camshaft phasing mechanism to a fixed camshaft sprocket and changes the angular position of the camshaft relative to the crankshaft.

It should be appreciated that the VCT system using an off-axis camshaft phasing device can also be implemented using a geared valvetrain. That is, rather than a VCT system that uses endless loops, such as belts and chains, to rotate sprockets the VCT system can use a plurality of sprockets that can directly contact each other and collectively communicate rotational energy from the crankshaft to the camshaft.

Turning to FIG. 1, an implementation of a VCT system 10 is shown. FIG. 1 is a profile view of a cylinder block 12 of an internal combustion engine (ICE), shown with the cylinder heads removed, having a crankshaft 14, an off-axis camshaft phasing device 16, and a single camshaft 18. A crankshaft sprocket 20 is connected to a distal end of the crankshaft 14 and includes a plurality of teeth 22 that extend along an outer circumferential surface of the crankshaft sprocket and are shaped to engage an endless loop. As the crankshaft 14 rotates with respect to the cylinder block 12, the crankshaft 14 also rotates the crankshaft sprocket 20 as well. The camshaft sprocket 24 is attached to a distal end of the camshaft 18 and includes a plurality of teeth 26 that extend along an outer circumference of the camshaft sprocket 24. The camshaft sprocket 24 generally includes twice as many teeth as are found on the outer circumferential surface of the crankshaft sprocket 20 given that each rotation of the camshaft 18 corresponds to two rotations of the crankshaft 14 in a four-stroke internal combustion engine.

In one implementation, the off-axis camshaft phasing device 16 can be attached to an internal combustion engine (ICE) at a location that is spaced apart from the camshaft 18 such that the off-axis camshaft phasing device 16 and the camshaft 18 rotate about different axes. The camshaft phasing device 16 could be attached to the ICE via an idler shaft or an engine accessory (not shown), such as a balance shaft, a water pump, an oil pump, or a fuel pump. The idler shaft may receive a pulley, a sprocket, or a gear, to provide a couple of examples. The camshaft phasing device 16 includes a first camshaft phasing sprocket 28 coupled to an input and a second camshaft phasing sprocket 30 coupled to an output. This is shown in FIGS. 2-3. Along a radially outward facing exterior surface, the first camshaft phasing sprocket 28 has a set of teeth 32 for mating with a first endless loop 36, which can be a timing chain or a belt. And the second camshaft phasing sprocket 30 has a set of teeth 34 for mating with a second endless loop 38, which also can be implemented using a timing chain or a belt. The first endless loop 36 can engage the teeth 22 of the crankshaft sprocket 20 and the teeth 32 of the first camshaft phasing sprocket 28 thereby transmitting rotational force from the crankshaft sprocket 20 to the first camshaft phasing sprocket 28. As shown in FIG. 1, the second endless loop 38 can engage the teeth 34 of the second camshaft phasing sprocket 30 and the teeth 26 of the camshaft sprocket 24 to transmit rotational force from the second camshaft phasing sprocket 30 to the camshaft sprocket 24.

Ultimately, the rotational force from the crankshaft sprocket 20 is communicated to the camshaft sprocket 24 through the first camshaft phasing sprocket 28 and the second camshaft phasing sprocket 30 of the off-axis camshaft phasing device 16. As the crankshaft 14 rotates and turns the crankshaft sprocket 20, the first endless loop 36 communicates rotational motion to the first camshaft phasing sprocket 28 and rotates the off-axis camshaft phasing device 16 about the idler shaft or engine accessory. The input of the off-axis camshaft phasing device 16 connected to the first camshaft phasing sprocket 28 transmits rotational force from the crankshaft 14 to the output of the camshaft phasing device 16 and the second camshaft phasing sprocket 30. As the camshaft phasing device 16 rotates in response to rotational force communicated from the crankshaft sprocket 20 to the first camshaft phasing sprocket 28, the second camshaft phasing sprocket 30 rotates as well transmitting the rotational force to the camshaft sprocket 24 through the second endless loop 38. The off-axis camshaft phasing can angularly displace the input attached to the first camshaft phaser sprocket 28 relative to the output attached to the second camshaft phaser sprocket 30 thereby changing the phase of the camshaft 14 relative to the camshaft 18.

The off-axis camshaft phasing device 16 can be implemented in a variety of different ways, and can be hydraulically- or electrically-actuated. In the implementation shown in FIG. 2, an off-axis camshaft phaser device 16 that is hydraulically controlled includes a rotor 40, having one or more radially extending vanes 42 that are acted on by pressurized fluid, and a stator 44. The rotor 40 can be angularly displaced with respect to the stator 44 in response to a controlled flow of fluid exerting force on the vane(s) 42 of the rotor 40. The rotor 40 can be rigidly linked to the first camshaft phasing sprocket 28 using any one of a variety of techniques, such as welding or mechanical fasteners. And the second camshaft phasing sprocket 30 can be rigidly linked with the stator 44. In this implementation, the stator 44 can be a housing that receives the rotor 40 within a fluid-filled cavity. As pressurized fluid is selectively directed against a surface of the vane(s) 42, the rotor 40 can be angularly displaced with respect to the stator 44 such that the first camshaft phasing sprocket 28 is angularly displaced with respect to the second camshaft phasing sprocket 30. The first camshaft phasing sprocket 28, the second camshaft phasing sprocket 30, and the entire off-axis camshaft phasing device 16 can rotate about an idler shaft 46 as the crankshaft sprocket 20 rotates. The first camshaft phasing sprocket 28 and the second camshaft phasing sprocket 30 can be configured such that they are axially-spaced relative to each other and rotate about a common axis (x) or are coaxial with each other.

Turning to FIG. 3, another implementation of the off-axis camshaft phasing device 16 that is electrically controlled is shown. The camshaft phasing device 16 shown in FIG. 3 includes the first camshaft phasing sprocket 28 that is rigidly linked to an input of the device 16 and a second camshaft phasing sprocket 30 that is rigidly linked to an output of the device 16. A mechanical gearbox 48 linked to the input and the output can vary the angular position of the first camshaft phasing sprocket 28 relative to the second camshaft phasing sprocket 30. It should be appreciated that the off-axis camshaft phasing device 16 that is electrically actuated can be implemented in a variety of different ways. For example, the off-axis phasing device 16 can use a planetary gearbox that engages a plurality of ring gears that each have radially inwardly facing gear teeth. An example of this type of camshaft phasing device is described in U.S. Patent Application Publication No. 2017/0248045 the entirety of which is incorporated by reference. The first camshaft phasing sprocket 28 can be rigidly linked to a first ring gear 50 and the second camshaft phasing sprocket 30 can be rigidly linked to a second ring gear 52. The first endless loop 36 shown in FIG. 1 can transmit rotational force from the camshaft sprocket 24 to the first camshaft phasing sprocket 28 and the second endless loop 38 can transmit rotational force from the off-axis camshaft phasing device 16 to the camshaft 18. As the crankshaft sprocket 20 rotates and communicates the rotational motion to the first camshaft phasing sprocket 28 via the first endless loop 36, the first ring gear 50 rotates along with the first camshaft phasing sprocket 28. The mechanical gearbox 48 that engages the ring gears 50, 52 can be rotated by an electric motor (not shown). When the output shaft of the electric motor, coupled to the mechanical gearbox 48, rotates the mechanical gearbox 48 at the same angular velocity as the ring gears 50, 52, the angular position of the first camshaft phasing sprocket 28 will be maintained relative to the second camshaft phasing sprocket 30. And when the output shaft of the electric motor rotates at an angular velocity that is higher or lower than the first camshaft phasing sprocket 28, the mechanical gearbox 48 can angularly displace the second ring gear 52 relative to the first ring gear 50 thereby angularly displacing the second camshaft phasing sprocket 30 relative to the first camshaft phasing sprocket 28. The displacement of the second camshaft phasing sprocket 30 relative to the first camshaft phasing sprocket 28 can advance or retard the timing of the camshaft 18 relative to the crankshaft 14.

Another implementation of a VCT system 100 is shown in FIG. 4. The VCT system 100 shown in FIG. 4 involves an ICE that uses a concentric camshaft 102 including an inner camshaft 104 and an outer camshaft 106 that can be moved angularly with respect to each other. An angular position of the inner camshaft 104 can be controlled by an inner off-axis camshaft phasing device 108 and an angular position of the outer camshaft 106 can be controlled by an outer off-axis camshaft phasing device 110. Concentric camshafts are known by those skilled in the art, an example of which is shown in FIG. 1 of U.S. Pat. No. 8,186,319 and described in column 6, lines 10-53; the contents of that portion of U.S. Pat. No. 8,186,319 are incorporated by reference. An inner fixed camshaft sprocket 114 can be rigidly linked to a distal end of the inner camshaft 104 and an outer fixed camshaft phasing sprocket 116 can be rigidly linked to a distal end of the outer camshaft 106. The inner fixed camshaft sprocket 114 can be axially spaced from the outer fixed camshaft sprocket 116 and rotate independently of each other such that the inner camshaft 104 and the outer camshaft 106 are rotated by separate endless loops engaged by separate camshaft phasing devices.

The inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 are separate camshaft phasers that are not rotationally coaxial with respect to the concentric camshaft 102 and are instead mounted off-axis relative to the camshaft axis of rotation. The inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 can be implemented using electrically- or hydraulically-actuated camshaft phasers as have been described above. The inner off-axis camshaft phasing device 108 includes a first inner camshaft phasing sprocket 118 and a second inner camshaft phasing sprocket 120 while the outer off-axis camshaft phasing device 110 includes a first outer camshaft phasing sprocket 122 and a second outer camshaft phasing sprocket 124. The ICE can include separate spindles, such as idler shafts, that the inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 attach to and rotate about during operation. And the axes about which the spindles rotate are not coaxial with the rotational axis of the camshaft.

The crankshaft 14 of the ICE can include a first crankshaft sprocket 126 and a second crankshaft sprocket 128 that are axially spaced from each other and attached to a distal end of the crankshaft 14. The first crankshaft sprocket 126 and the second crankshaft sprocket 128 can each include a plurality of radially outwardly facing teeth 130 that are shaped to engage an endless loop such as a chain or a belt. The first inner camshaft phasing sprocket 118 and the second inner camshaft phasing sprocket 120 as well as the first outer camshaft phasing sprocket 122 and the second outer camshaft phasing sprocket 124 can each have a plurality of radially outwardly facing teeth 132 that are shaped to engage an endless loop. A first endless loop 134 can engage the teeth 130 of the first crankshaft sprocket 126 and the first inner camshaft phasing sprocket 118 while a second endless loop 136 can engage the teeth 130 of the second crankshaft sprocket 128 and the first outer camshaft phasing sprocket 122. A third endless loop 138 can engage the teeth 132 of the second inner camshaft phasing sprocket 120 and the teeth 140 of the inner fixed camshaft sprocket 114 transmitting rotational force to the inner camshaft 104 while a fourth endless loop 142 can engage the teeth 132 of the second outer camshaft phasing sprocket 124 and the teeth 140 of the outer fixed camshaft sprocket 116 transmitting rotational force to the outer camshaft 106.

As the crankshaft 14 rotates, the first crankshaft sprocket 126 and the second crankshaft sprocket 128 communicate rotational force to the first inner camshaft phasing sprocket 118 and the first outer camshaft phasing sprocket 122, respectively. The rotational force received by the first camshaft phasing sprockets 118, 122 can rotate the inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 about their respective spindles. The rotation of the inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 also rotates the second inner camshaft phasing sprocket 120 and the second outer camshaft phasing sprocket 124 thereby rotating the inner camshaft 104 and the outer camshaft 106 through the third endless loop 138 and the fourth endless loop 142, respectively. The inner off-axis camshaft phasing device 108 can change the angular position of the inner camshaft 104 independent of the angular position of the outer camshaft 106 by changing the angular position of the first inner camshaft phasing sprocket 118 relative to the second inner camshaft phasing sprocket 120. Similarly, the outer off-axis camshaft phasing device 110 can change the angular position of the outer camshaft 106 independent of the angular position of the inner camshaft 104 by changing the angular position of the first outer camshaft phasing sprocket 122 relative to the second outer camshaft phasing sprocket 124. The second inner camshaft phasing sprocket 120, as it changes its angular position relative to the first inner camshaft phasing sprocket 118 communicates that change in relative angular position to the inner fixed camshaft sprocket 114 through the third endless loop 138. And the second outer camshaft phasing sprocket 124, as it changes its angular position relative to the first outer camshaft phasing sprocket 122, communicates that change in relative angular position to the outer fixed camshaft sprocket 116 through the fourth endless loop 142. Changes to the angular position of the inner camshaft 104 relative to the crankshaft 14 or to the angular position of the outer camshaft 106 relative to the crankshaft 14, or what also may be referred to as a change in phase, can be carried out independent of each other.

FIG. 5 depicts another implementation of a VCT system 150. The VCT system 150 shown in FIG. 5 includes concentric camshafts comprising an inner camshaft and an outer camshaft, two separate camshaft phasing devices, and three endless loops. An angular position of the inner camshaft 104 can be controlled by the inner off-axis camshaft phasing device 108 and an angular position of the outer camshaft 106 can be controlled by the outer off-axis camshaft phasing device. The inner fixed camshaft sprocket 114 can be rigidly linked to a distal end of the inner camshaft 104 and the outer fixed camshaft phasing sprocket 116 can be rigidly linked to a distal end of the outer camshaft 106. The inner fixed camshaft sprocket 114 can be axially spaced from the outer fixed phasing sprocket 116 and rotate independently of each other such that the inner camshaft 104 and the outer camshaft 106 are rotated by separate endless loops engaged by separate camshaft phasing devices.

The inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 are separate camshaft phasers that are not rotationally coaxial with respect to the concentric camshaft(s) 102 and are instead mounted off-axis relative to the camshaft axis of rotation. The inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 can be implemented using electrically- or hydraulically-actuated camshaft phasers as have been described above. The inner off-axis camshaft phasing device 108 includes a first inner camshaft phasing sprocket 118 and a second inner camshaft phasing sprocket 120 while the outer off-axis camshaft phasing device 110 includes a first outer camshaft phasing sprocket 122 and a second outer camshaft phasing sprocket 124. The ICE can include separate spindles that the inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 attach to and rotate about during operation. And the axes about which the spindles rotate are not coaxial with the rotational axis of the concentric camshafts 102.

The crankshaft 14 of the ICE can include a crankshaft sprocket 20 that is attached to a distal end of the crankshaft 14. The crankshaft sprocket 20 includes a plurality of radially outwardly facing teeth 22 that are shaped to engage a first endless loop 152 such as a chain or a belt. The first inner camshaft phasing sprocket 118 and the second inner camshaft phasing sprocket 120 as well as the first outer camshaft phasing sprocket 122 and the second outer camshaft phasing sprocket 124 can each have a plurality of racially outwardly facing teeth 132 that are shaped to engage the endless loop 152. The first endless loop 152 can engage the teeth of the crankshaft sprocket 20, the first inner camshaft phasing sprocket 118, and the first outer camshaft phasing sprocket 122. As the crankshaft 14 rotates, the first endless loop 152 simultaneously applies rotational force to the first inner camshaft phasing sprocket 118 and the first outer camshaft phasing sprocket 122. A second endless loop 154 can engage the teeth 132 of the second inner camshaft phasing sprocket 120 and the teeth 132 of the inner fixed camshaft sprocket 114 transmitting rotational force to the inner camshaft 104 while a third endless loop 156 can engage the teeth 132 of the second outer camshaft phasing sprocket 124 and the teeth 132 of the outer fixed camshaft sprocket 116 transmitting rotational force to the outer camshaft 106.

As the crankshaft 14 rotates, the crankshaft sprocket 20 communicates rotational force to the first inner camshaft phasing sprocket 118 and the first outer camshaft phasing sprocket 122, respectively. The rotational force received by the first camshaft phasing sprockets 118,122 can rotate both the inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 about their respective spindles. The rotation of the inner off-axis camshaft phasing device 108 and the outer off-axis camshaft phasing device 110 also rotates the second inner camshaft phasing sprocket 120 and the second outer camshaft phasing sprocket 124 thereby rotating the inner camshaft 104 and the outer camshaft 106 through the second endless loop 154 and the third endless loop 156, respectively. The inner off-axis camshaft phasing device 108 can change the angular position of the inner camshaft 104 independent of the angular position of the outer camshaft 106 by changing the angular position of the first inner camshaft phasing sprocket 118 relative to the second inner camshaft phasing sprocket 120. Similarly, the outer off-axis camshaft phasing device 110 can change the angular position of the outer camshaft 106 independent of the angular position of the inner camshaft 104 by changing the angular position of the first outer camshaft phasing sprocket 122 relative to the second outer camshaft phasing sprocket 124. The second inner camshaft phasing sprocket 120, as it changes its angular position relative to the first inner camshaft phasing sprocket 118 communicates that change in relative angular position to the inner fixed camshaft sprocket 114 through the second endless loop 154. And the second outer camshaft phasing sprocket 124, as it changes its angular position relative to the first outer camshaft phasing sprocket 122 communicates that change in relative angular position to the outer fixed camshaft sprocket 116 through the third endless loop 156. Changes to the angular position of the inner camshaft 104 relative to the crankshaft 14 or to the angular position of the outer camshaft 106 relative to the crankshaft 14 can be carried out independent of each other.

Other implementations of the VCT system are possible. For example, the sprockets described above can include radially-outwardly facing gear teeth that directly engage with other sprockets having gear teeth to communicate rotational energy from a crankshaft to one or more camshafts through one or more off-axis camshaft phasing devices. For example, ICEs can implement valvetrain systems that include a geared timing drive. Rather than relying on a plurality of endless loops to connect each sprocket, the sprockets can engage each other, either directly or through one or more idler gears, to communicate rotational force from the crankshaft sprocket to one or more camshaft phasing devices. The crankshaft can include a crankshaft sprocket on a distal end that includes radially outwardly facing gear teeth shaped to engage one or more other sprockets with similar radially-outwardly facing gear teeth. The VCT system can use one or more camshaft phasing devices that include a first camshaft phasing sprocket connected to an input and a second camshaft phasing sprocket connected to an output such that each of the sprockets include radially-outwardly facing gear teeth shaped to engage and transmit rotational force to other sprockets having similar radially-outwardly facing gear teeth. In on implementation, a camshaft can include a camshaft sprocket with gear teeth that directly engage a camshaft phasing sprocket or through one or more idler gears. The use of sprockets having gears that directly contact other gears can eliminate the use of endless loops.

It is to be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiments) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.

As used in this specification and claims, the terms “e.g.,” “for example,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation. 

What is claimed is:
 1. A variable camshaft timing system, comprising: a camshaft phasing mechanism that selectively changes an angular position of an input relative to an output; a first camshaft phaser sprocket, coupled with the input of the camshaft phasing mechanism, configured to engage a first endless loop that communicates rotational force from a crankshaft to the input of the camshaft phasing mechanism; and a second camshaft phaser sprocket, axially spaced from the first camshaft phaser sprocket and coupled with the output of the camshaft phasing mechanism, configured to engage a second endless loop that communicates rotational force from the output of the camshaft phasing mechanism to a camshaft and change the angular position of the camshaft relative to the crankshaft, wherein the camshaft phasing mechanism is mounted about an axis that is different from an axis of camshaft rotation.
 2. The variable camshaft timing system recited in claim 1, wherein the first camshaft phaser sprocket and the second camshaft phaser sprocket rotate about a common axis.
 3. The variable camshaft timing system recited in claim 1, wherein the camshaft phasing mechanism is hydraulically-actuated.
 4. The variable camshaft timing system recited in claim 1, wherein the camshaft phasing mechanism is electrically-actuated.
 5. The variable camshaft timing system recited in claim 1, wherein at least one of the first endless loop or the second endless loop is a chain.
 6. The variable camshaft timing system recited in claim 1, wherein the camshaft phasing mechanism is attached to an internal combustion engine by an idler shaft or an engine accessory.
 7. A variable camshaft timing system, comprising: a camshaft phasing mechanism that selectively changes an angular position of an input relative to an output; a first camshaft phaser sprocket, coupled with the input of the camshaft phasing mechanism, configured to receive rotational force from a crankshaft; and a second camshaft phaser sprocket, axially spaced from the first camshaft phaser sprocket and coupled to the output of the camshaft phasing mechanism, configured to provide rotational force to a camshaft and change the angular position of the camshaft relative to the crankshaft, wherein the variable camshaft timing device is mounted about an axis that is different from an axis of camshaft rotation.
 8. The variable camshaft timing system recited in claim 7, wherein the first camshaft phaser sprocket, the second camshaft phaser sprocket, or both directly engage one or more gears.
 9. The variable camshaft timing system recited in claim 7, wherein the first camshaft phaser sprocket and the second camshaft phaser sprocket each engage an endless loop.
 10. The variable camshaft timing system recited in claim 7, wherein the first camshaft phaser sprocket and the second camshaft phaser sprocket rotate about a common axis.
 11. The variable camshaft timing system recited in claim 7, wherein the camshaft phasing mechanism is hydraulically-actuated.
 12. The variable camshaft timing system recited in claim 7, wherein the camshaft phasing mechanism is electrically-actuated.
 13. The variable camshaft timing system recited in claim 7, wherein the camshaft phasing mechanism is attached to an internal combustion engine by an idler shaft or an engine accessory.
 14. A variable camshaft timing system, comprising: an inner camshaft phasing mechanism that selectively changes an angular position of an inner camshaft phasing mechanism input relative to an inner camshaft phasing mechanism output; a first inner camshaft phaser sprocket, coupled with the inner camshaft phasing mechanism input, configured to engage an endless loop that communicates rotational force from a crankshaft to the inner camshaft phasing mechanism input; and a second inner camshaft phaser sprocket, axially spaced from the first inner camshaft phaser sprocket and coupled with the inner camshaft phasing mechanism output, configured to engage an inner camshaft endless loop that communicates rotational force from the inner camshaft phasing mechanism output to an inner camshaft; an outer camshaft phasing mechanism that selectively changes an angular position of an outer camshaft phasing mechanism input relative to an outer camshaft phasing mechanism output; a first outer camshaft phaser sprocket, coupled with the outer camshaft phasing mechanism input, configured to engage an endless loop that communicates rotational force from the crankshaft to the outer camshaft phasing mechanism input; and a second outer camshaft phaser sprocket, axially spaced from the first outer camshaft phaser sprocket and coupled with the outer camshaft phasing mechanism output, configured to engage an outer camshaft endless loop that communicates rotational force from the outer camshaft phasing mechanism output to an outer camshaft, wherein the inner camshaft and the outer camshaft are concentric.
 15. The variable camshaft timing system recited in claim 14, wherein a single endless loop engages the first inner camshaft phaser sprocket and the first outer camshaft phaser sprocket.
 16. The variable camshaft timing system recited in claim 14, wherein the inner camshaft phasing mechanism and the outer camshaft phasing mechanism are hydraulically-actuated.
 17. The variable camshaft timing system recited in claim 14, wherein the inner camshaft phasing mechanism and the outer camshaft phasing mechanism are electrically-actuated.
 18. The variable camshaft timing system recited in claim 14, wherein at least one of the endless loops is a chain.
 19. The variable camshaft timing system recited in claim 14, wherein the camshaft phasing mechanism is attached to an internal combustion engine by an idler shaft or an engine accessory. 